1. Field of the Invention
The present invention relates generally to an improved method and apparatus for disposing of leachate, including an improved method and apparatus for disposing of landfill produced leachate using landfill produced gases as fuel.
2. Brief Description of the Prior Art
Various gases are produced from the degradation of buried waste in landfills. These gases can be noxious, malodorous, flammable and/or potentially dangerous. Such gas can be withdrawn from the landfills and combusted in a flare whereby noxious components of the gases are oxidized into normal products of combustion before being released into the atmosphere.
Landfill leachates are produced from surface water and rainwater percolating through the buried waste or coming in contact with waste in landfills, thereby mixing noxious compounds into the liquid. This leachate can pollute other nearby water sources by seeping through the ground, therefore, it is generally desirable and necessary to remove the leachate before the water supplies are polluted. Extracted leachate can be safely disposed of by either storing the leachate in tanks (which does not eliminate the problem, but only contains it), transporting the leachate to a waste water treatment facility (which is costly), or treating the leachate on-site. A preferred method of treating leachate, and the focus of this invention, thermally changes the state of, then thermally incinerates the vaporized leachate using landfill gases as fuel.
Current methods of vaporizing leachate using landfill gas as fuel have several drawbacks. First, the evaporation chambers are not pressurized, therefore, leachate vapors leave the chamber at or near its condensation temperature and quickly return back to its liquid state. Also, open flues in the evaporation chamber allow burning gases and leachate vapor to mix which prevents separate downstream environmental control systems to deal with the two different toxic sources. In addition, open flues create the possibility of leachate backing up into and damaging the burner, especially if pressurized. The present invention overcomes these shortfalls.
SUMMARY OF THE INVENTION
The present invention describes a method and apparatus for the vaporizing and thermal incineration of leachate utilizing gas. Particularly, the present invention can be used for effectively disposing of landfill leachate using landfill gas. The method of disposing of the leachate and gas comprises the steps of combusting gas (including landfill gas or any other waste or fuel gas) in a fire tube heater submerged in leachate (including landfill leachate) contained in a pressure-controlled tank, vaporizing the leachate with thermal energy absorbed from the fire tube heater, releasing the resulting leachate vapor through a pressure valve to a connecting enclosed thermal incinerator, and combusting the noxious leachate vapor in the thermal incinerator to thermally destroy volatile organics in the vapor and render the vapor environmentally acceptable.
Another object of this invention is to thermally destroy volatile organics in the landfill gas by oxidizing the volatile organics in the gas through combustion of the gas in the fire tube heater.
Another object of the invention is to direct landfill gas exhaust from the fire tube heater to the flare as a method of achieving a single point source emission, which may be required by permitting authorities.
Another object of the invention includes conditioning the landfill gas in a gas conditioning system to improve the combustion efficiency of the gas.
Another object of the invention is to maintain an acceptable level of leachate in the pressure-controlled tank. This is accomplished by pumping more leachate into the tank from a leachate storage tank or other holding facilities as leachate in the tank is vaporized and released from the tank. Excess leachate may also escape through a leachate overflow outlet.
Another object of this invention is to release pressure from the tank through a relief valve when the pressure in the tank becomes too high. Escaping vapor may be directed to a flare or other thermal incinerator for combustion.
The present invention also discloses the physical elements needed to construct an apparatus to carry out the aforementioned objects. The basic apparatus comprises a tank, a flame tube positioned in the tank, a burner attached to the flame tube, and a pressure-controlled vapor outlet connected to the top of the tank. Other objects of the invention may be carried out using a thermal incinerator, a gas source, a gas conditioning system, a closeable leachate inlet, a leachate outlet, a leachate storage tank or other storage facilities, a leachate control system, a horizontal support plate, and a relief pressure valve.
Another object of this invention is to combust leachate vapors utilizing gas fuels (including waste gas like landfill gas) as a combustion fuel in a thermal incinerator.
Another object of the invention is to create a waste disposal system for leachate that is completely self-sufficient. This is accomplished by attaching an asynchronous power generator to the electrical distribution systems of the landfill. The generator is powered by an internal combustion engine utilizing conditioned landfill gas or other fuel sources as fuel and generates electrical power and combusted gas exhaust. The electric powered devices and its control systems can utilize the electric power, with any excess power being utilized for other applications, placed into the electric supply grid or sold back to the electric supply grid. The gas exhaust can be directed to the flare so that additional volatile organics may be further thermally destroyed at a single source point outlet.
Another object of this invention is to provide a leachate thermal incineration system where the combusting gas does not mix with the leachate or the leachate vapors. This allows further downstream cleaning of the two different waste streams which may contain different volatile organics. In addition, by separating the leachate from the burning gas in the flame tube, the tank can be pressurized without fear of backing the leachate into the burner system.
Another object of this invention is to provide a pressurized tank for vaporizing leachate. Leachate vapor under pressure reaches a higher temperature than non-pressurized vapor before it is released from the tank. The higher temperature allows the leachate vapor to travel a further distance to a thermal incinerator where the vapor is oxidized before the vapor can condense back into liquid leachate.
Another object of this invention is to provide a single source outlet for all emissions before being released into the atmosphere.
It is another object of this invention to provide a continuous process for disposing of leachate. By continuously pumping new leachate into the tank, the process never needs to be stopped except for normal maintenance.
Another object of this invention is to maximize heat transfer from the combusting gas to the liquid leachate by keeping the flame tube submerged in the middle of the leachate in the tank.
Another object of this invention is to efficiently utilize all available landfill or other on-site waste by-products in order to meet federal environmental regulations and incentives.